Burette with removable stopcock formed of synthetic resin



M y 9, 1970 M. A. CRAIG ETAL 3,512,944

BURETTE WITH REMOVABLE STOPCOCK FORMED OF SYNTHETIC RESIN Filed Sept. 13, 1967 I! I!!! W! WI BY WALTER l. HOLMS WM p 9 M AGENT United States Patent 3,512,944 BURETTE WITH REMOVABLE STOPCOCK FORMED OF SYNTHETIC RESIN Michael A. Craig, Corning, and Walter I. Holms, Elmira, N.Y., assignors to Corning Glass Works, Corning, N.Y., a corporation of New York Filed Sept. 13, 1967, Ser. No. 667,460 Int. Cl. B01l 3/02; F16]; 5/04 US. Cl. 23-292 4 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The present invention relates to the construction of laboratory burettes for the delivery and measurement of fluids. Such burettes conventionally comprise a glass cylinder having markings thereon to indicate volumetric gradations and a stopcock separating the cylinder from the delivery tip of the burette. The cylinder, the outer shell of the stopcock and the delivery tip are conventionally formed as an integral glass body, and a stopcock plug having a fluid-flow channel extending therethrough is rotatably mounted in the stopcock shell.

Burettes formed in the conventional manner are expensive to manufacture, and replacement costs are high, inasmuch as damage to either the cylinder, the stopcock shell or the delivery tip requires replacement of three integral portions. Furthermore, it is necessary that the inner surface of the glass stopcock shell be ground, which adds to the expense of the burette.

Accordingly, it is an object of the present invention to provide a novel burette in which construction and replacement costs are minimized.

A further object is the provision of a burette which permits substitution of graduated cylinders, or other fluid containers, of varying capacities, without the necessity for changing the other components of the burette.

SUMMARY OF THE INVENTION The objects of the invention are accomplished by the provision of a burette comprising a fluid container and a delivery tip joined by a stopcock held in removable interference-fitted engagement therewith, both the shell and the plug of the stopcock being formed of a chemically inert synthetic resin. Due to the separability of the components of the burette, breakage of either the fluid container or the delivery end does not necessitate replacement of the stopcock, and easy substitution of parts may be effected.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a longitudinal sectional view of a burette according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a burette constructed according to the preferred embodiment of the invention comprises glass graduated cylinder 10, stopcock 12 and glass delivery tip 14. Stopcock 12 comprises shell 16 and cylindrical plug 18 rotatably mounted in bore 19 of the shell ice and maintained in position by means of rubber O-rings 20. Both the shell and the plug are formed of polytetrafiuoroethylene, and a fluid-tight seal is maintained between the plug and thebore of the shell. Shell channel 22 extends through shell 16 in a longitudinal direction and forms a fluid-flow channel from graduated cylinder 10 to delivery tip 14 when plug 18 is in the illustrated position with plug channel 24 aligned with the shell channel. Plug 18 is rotatable by means of handle 25. Shell 16 has at its upper end a cylindrical male portion 26 which extends into the lower end of graduated cylinder 10 and is in fluid-tight interference-fitted engagement with the inner surface thereof. At the lower end of plug 16 is a cylindrical female portion 27 having an inside diameter smaller than the outside diameter of male portion 26. The upper end of delivery tip 14 projects into portion 27 and holds the delivery tip in fluid-tight interference-fitted engagement.

Stopcock shell 16 and plug 18 may be formed of other chemically inert, nonporous, nonabsorbent relatively hard and generally form-retaining wax-like synthetic resins which are slightly elastic under low stress and which are self-lubricating with respect to the surfaces of similar materials. Other such materials in addition to polytetrafiuoroethylene are polystyrene and polytrifluorochloroethylene.

While this invention has been described in connection with possible forms or embodiments thereof, it is to be understood that the present disclosure is illustrative rather than restrictive and that changes or modifications may be resorted to without departing from the spirit of the invention.

We claim:

1. A burette assembly for the delivery of fluids, said assembly comprising:

a container for fluids having a cylindrical portion at the lower end thereof,

a tubular delivery tip having a cylindrical portion at the upper end thereof, and

a stopcock removably interposed between said container and delivery tip, comprising a shell having a bore extending therethrough, a plug rotatably mounted in said bore and means for rotating said plug in said shell, said shell and said plug having channels extending therethrough so as to form a continuous channel for fluid flow between said container and said delivery tip at one position of said plug in said shell, wherein the improvement comprises:

(a) said shell and said plug of said stopcock being formed of a chemically inert, nonporous, nonabsorbent, relatively hard and generally form-retaining wax-like synthetic resin which is slightly elastic under low stress and which is self-lubricating with respect to surfaces of similar materials;

(b) said stopcock shell including a cylindrical male portion on its upper end positioned within the cylindrical portion of said container in fluidtight removable interference-fitted engagement with inner surface portion of said container;

(c) said stopcock shell further including, a cylindrical female portion on its lower end, the cylindrical upper end of said delivery tip positioned within said cylindrical female portion in fluidtight removable interference-fitted engagement therewith, a lower section of said female portion protectively overlying the upper end portion of said delivery tip; the outside diameter of said male portion differing from the inside diameterof said female portion; (d) said rotatably mounted cylindrical plug being means of retaining rings secured to said plug,

with the inner side surfaces of said retaining rings contacting the outside surface of said stopcock shell. 2. The burette assembly of claim 1 wherein said shell and said plug are comprised of polyetetrafiuoroethylene. 3. The burette assembly of claim 1 wherein the inside diameter of said stopcock shell female portion is smaller than the outside diameter of said male portion thereof.

4. The burette assembly of claim 1 wherein said retaining rings are rubber O-rings.

Refer-ences Cited UNITED STATES PATENTS 6/1961 Gilmont 23-292XR 6/1967 Phillips 23-292 MORRIS o. WOLK, Primary Examiner R. M. REESE, Assistant Examiner 7 US. Cl. X.R-. 251368 

